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astrobiology

We’ve long known that there was an ocean or something very much like it under the icy crust of the Jovian moon Europa, and that this icy wasteland offers one of the best chances to find life in our solar system despite living in a very turbulent and radioactive neighborhood. And now, the same astronomer who stunned Pluto before the IAU’s planetary double-tap, Mike Brown, found strong evidence that Europa’s ocean is leaking to the surface and is salty like ours. Basically, a short summary of the elegant details I encourage you to read from Dr. Brown himself is that the chemical residues on the moon’s surface match up with exactly what we’d expect if it had a thick, salty, liquid ocean which periodically rises through the cracks in the ice and leaves deposits as it recedes with the tides. We could learn even more, but radiation scatters other compounds we could measure from our post right here on the blue marble. So far, though, so good for bacteria and multicellular colonies that could potentially call Europa home.

Now it’s very important to know that organic chemical signatures do not always mean life and a distinct lack of experience with alien organisms on our part means that until we actually see one with our probes and run several hundred tests and a few thousand reviews of the data from all those tests, we won’t know if we found alien organisms. Well, unless an alien fish just wiggles to the camera and waves hello. That would speed up the announcement. But in all seriousness, as far as cases for promising habitats go, everything we find about Europa makes it look better and better for exploration. The only problem is that the ocean where so much life could exist lies so far down, in some cases under several miles of ice. Drilling through it is complicated and really dangerous for robotic probes, so the focus has been on trying to get access to the ocean with a minimum of digging, using something like a rover with a tiny submarine to explore the shallows. If what Brown has found is any indication, we might find even more about Europa’s chemistry this way since some of the more scientifically interesting chemicals could just float up to us.

However, keep in mind that the moon’s surface is bathed by radiation and microorganisms that evolve under several miles of ice and meters of water would be instantly fried to a crisp if they’re exposed to it, leaving promising but ambiguous residue on the surface. For anything more alien and complex than extremophiles that may have even survived the trip from Earth, we will need to be ready to dive deep and look far and wide. It’s actually another reason for human exploration of the outer solar system. Robots can only be made so clever in space, and they’re not good at dealing with the unknown and the uncertain, having no instinct or useful previous experiences from which to make decisions about new environments. Having humans guide them as they look for alien life on an unknown, largely unfamiliar world would be a terrific fusion of our brainpower and machine endurance that could lead to something as big as proof that we’re not alone. That knowledge alone should justify the effort of making the trip.

Another day, another study identifying more potentially habitable worlds in the Kepler data, this time by professional astronomers and volunteers called the Planet Hunters who discussed their planet detections on a specialized message board system called Talk. What they found was that more gas giants orbited stars in their habitable zones than initially thought, giving real evidence for the hypothesis that while alien Earths could be somewhat rare, moons orbiting alien Jupiters and Saturns may be a fairly common habitat for extraterrestrial life. Trouble is that we can’t see these moons or detect the wobble of the planets they orbit, so we don’t know how many of them there are, how big they are on average, and their likely composition. However, we do have very good reasons to assume that they could be there since gas giants in our own solar system are swarmed by moons of all shapes and sizes, and some are very possible hosts to life.

So one would think that a moon big enough to hold on to an atmosphere that’s not too dense or composed mainly of greenhouse gases in an alien star’s habitable zone would have liquid water in significant quantities. Even better, it would feel the gravitational tides of a gas giant that would in effect knead its interior, promoting volcanism, circulating rich organic matter that could either kick start living things or fuel them. Think of Io but more subdued and covered with oceans and small continents, or Titan without the mind-numbing cold. It could be a perfect habitat, and given billions of years, maybe even evolve intelligent life. But there’s a potential problem here. Typical solar system formation models dictate that rocky worlds form closer to a star than gas giants, so to be in the habitable zone of the vast majority of stars out there, alien Jupiters had to drift into these orbits, pushing out rocky worlds and reshuffling their siblings. What would that do to their moons? Would they be collateral damage in the upheaval of the solar system?

Ideally, the immense gravity of these gas giants would push planets aside as they spiral into the habitable zone and their clutches of icy rocks would slowly thaw to host oceans and fertile land for life to start taking hold. But again, the only way we’ll know this is if we build bigger and more powerful telescopes to detect their presence and hopefully one day resolve them as pixels for a quick spectrographic sniff of their atmospheres. Maybe, just maybe, decades from now, a future astronomer and a crew of enthusiastic volunteers will be looking through a data set collected by the latest planet hunting telescope and find a little bluish pixel next to a gas giant, or readings of a gas pointing to a stable biosphere, like oxygen from a recently discovered alien moon. It won’t be Earth 2.0, but it will be just as important, and we’ll be able to look up at the night sky knowing that we’re not alone because somewhere, a weird world with a killer view of a turbulent gas giant is home to something that can look back at Earth, even if it won’t wonder about us…

In some ways the motivation for proposing this kind of cosmic panspermia is a little dated. It comes from a time when we felt that the origin of life of on Earth was such a mystery, and such an unlikely event, that it was convenient to outsource it. Although this didn’t actually solve the real question of life’s origins, it meant that a specific origin ‘event’ could be extremely rare among the 200 billion stars of the Milky Way yet life would still show up in other places.

These days I think our discoveries about the remarkable abundance and diversity of so-called pre-biotic chemistry […] in every nook and cranny of our solar system, and even in the proto-stellar nebula of other stars and the wilds of interstellar space – swings the pendulum back to Earth. Nature seems adept at making all the pieces for life, apparently raising the odds of local bio-genesis.

How are these two thoughts connected again? I’m not exactly sure how life being very adaptable would mean that it raises the odds of Earth being its origin because we’re talking about evolution rather than abiogenesis. Caleb Scharf, the scientist who wrote the post, seems to be making the same kind of mistake many creationists do when trying to ridicule evolutionary theory by asking how life would’ve come from non-life and nothing that evolution fails to answer this question. So it’s little wonder that whatever life gets here or starts here would fill every available nook, cranny, and environmental niche since natural selection would favor their reproduction. But whether the origin of these species is on Earth or in space is more or less a toss-up if we’re considering just how well they adapted to their current environments.

Yes, we could say that it’s more likely that life originated on Earth because space is vast and the odds of enough comets and asteroids hitting the planet at just the right conditions for life to take hold are astronomical, literally, so it makes sense to look for an explanation that makes life more likely to arise here. That explanation may not be right, but we don’t have a complete picture of how it came to be and so we’re still trying to find viable ideas that seem to fit the evidence we’ve observed so far. But an important part of the process is not to discard hypotheses without any evidence that they simply don’t fit with the observations, something that Scharf does with an odd certainty about the habitability of promising places in the solar system by hearty microorganisms that should dominate the universe based on the way natural selection works.

But the problem, and the potential paradox, is that if evolved galactic panspermia is real it’ll be capable of living just about everywhere. There should be [organisms] on the Moon, Mars, Europa, Ganymede, Titan, Enceladus, minor planets and cometary nuclei. Every icy nook and cranny in our solar system should be a veritable paradise for these ultra-tough life forms, honed by natural selection to make the most of [the] appalling conditions. So if galactic panspermia exists why haven’t we noticed it yet?

He then goes on to answer his own question by saying that we probably haven’t looked all that hard in all these places, don’t know for what we’re really looking, or possibly both, and ponders would it would mean if we kept searching and found nothing. You can tell that he’s really pushing for the Earth-centric explanation and again, as elaborated above, I can see why, but his primary reason for pushing it seems to be based on a very strange confusion between abiogenesis and natural selection with no facts to back it up. The argument seems to be: we know more extreme organisms on Earth, natural selection seems to be doing it’s job, we haven’t explored all of the promising candidates for life in our solar system in sufficient detail and we don’t really know what we’re trying to find and how we’ll know we found it, therefore, life arose on Earth. Doesn’t seem like a scientific train of thought to me, especially with all the evidence that there was at least an important role being played by organic matter or microorganisms from space…

According to results from Kepler, there’s another habitable planet just 49 light years away. Well, mostly habitable by something. Gliese 163c is on the higher end of the super-earth label, coming in at between 1.8 and 2.4 times the size of Earth and almost 7 times its mass, and orbiting a red dwarf star once every 26 days. It’s hot, about 60° C hot according to a baseline estimate, but it’s not too hot for a lot of living things. All sorts of extremophiles live in much hotter temperatures on our own world, considering boiling hot caves and toxic vents a cozy home. This is why the press releases from the discoverers of the solar system focused on the potential for microbial or rather simple animal life on Gliese 163c, pointing out that on Earth, no plants or animals can survive for extended periods of time when temperatures soar past 50° C, which would be a cool day on the alien world in question. However, with all due caution, we should consider that what seems to be extreme to us isn’t all that extreme to many other lifeforms and complex life that had billions and billions of years to evolve in very hot conditions could certainly find a way to thrive.

Even more importantly, we don’t know the composition of Gliese 163c’s air, and that could be a critical factor in deciding how habitable we deem it. If its atmosphere is primarily filled with water vapor or has huge concentrations of greenhouse gases, it may as well be another Venus and a hellish place for even the most primitive life. But on the other hand, only small quantities of any greenhouse gases would mean that the planet doesn’t retain very much heat. Water would be a great heat sink as well, and considering that it’s almost certainly tidally locked, the movement of air between the day side and the night side could bring down the overall global temperature and open up some very cool and cozy environments for complex, multicellular life. And as always, if you go deep enough into an ocean, there are bound to be places for life to find a niche, even if the planet is drifting though interstellar space with no sun to warm it. A few hundred meters under the seas of Gliese 163c it could be nice and cool for large aquatic animals to roam in search of food and a mate, though they might have to avoid choppy seas around any equatorial storms fueled by constant evaporation on the day side.

Ideally, the center of the planet’s day side would be a bone dry, perpetual desert constantly in the blinding gaze of its parent star. With no water to evaporate, no cycles of cooling and heating because there would be no night, and nothing but barren rocks, the worst its sun can do is kick up massive dust storms around the equator. That would leave seas, lakes, or even oceans free of constant monsoons. Of course this is pure speculation, but the possibilities are there and we now have a nearby target to better investigate for signs of biology. Next, we can sample its air to better figure out its real average temperature, and try to take a snapshot of what it actually looks like. Its doubtful that we could make out seas or continents with what would most likely be a tiny fraction of a pixel on the screen, but the reflectivity of its clouds or lack thereof could tell us a bit about Gliese 163c’s composition. And that’s the exciting part of astronomy. Every peek we take, every survey we conduct has the potential to show us something new or overturn our notions of what can happen in the cosmos. After all, the world’s top experts thought that the universe was static and infinite until one of them took another look and made a few measurements…

Say that somewhere out there is a species of space-faring aliens which have relativistic rockets or warp drive technology that lets it travel between solar systems. Considering the sheer size of the universe, it’s probably a good bet that at least one exists. And as these aliens are tooling around, their spacecraft will likely leave what we could call a wake in the fabric of space and time, a wake that we could observe under the right conditions, when the stars align. This is the main gist of an arXiv paper which considers that despite the possibilities of a successful detection of an alien craft’s fly-by being almost nil, we could still try just in case we do get lucky. To start a long term survey, we just need to find star pairs close to each other and aligned with the Earth at about the right angle to give us a good view of the space between them. Then we just look and wait for something to show up, ideally a smear of light magnified by the relativistic wake of the spacecraft we’re trying to detect. It’s a neat idea and the authors readily acknowledge that we may just be too far away to notice alien travelers, or be in a region of space where there are no civilizations capable of interstellar travel, which keeps them grounded when discussing such a lofty SETI approach. But there is one thing they may want to explore a little further…

When we last discussed the Icarus project, did you notice the sheer size of the probe being considered? Go and have a look at that monstrosity and note that the Empire Stare Building does not look all that much bigger by comparison. That’s not because Icarus’ designers have a thing for really large spacecraft, it’s because this craft will have to carry so much fuel and have giant engines to accelerate. Any future interstellar craft designed to support humans, would be even bigger than Icarus to carry all the essentials across trillions and trillions of miles. Let’s say that at some point, we’ll actually decide to build a ship able to ferry humans between the Sun and Alpha Centauri at relativistic speeds, and equip it with a brand new, state of the art artificial black hole engine which should get us up to relativistic speeds very, nicely, shaving the travel time down to only a couple of years instead of several millennia. We’d need to build something much like the Burj Khalifa tower in Dubai to house all the things necessary to comfortably support and house our crew, then get another pair of similar structures and devote them to being engines and fuel tanks, and at least another one to function as a backup tank and to securely house all the shuttle craft that will let the crew go down to the surface of their target world because that giant assembly is simply never going to be able to land. It’s far too huge and heavy. And keep in mind that these estimates are probably erring on the small side, relying on a radical propulsion system.

Now, our imaginary spaceship which we’ll call something inspiring, say, The Really, Really Huge, would have an approximate mass of 2 million tons empty and without the micro black hole suspended between the giant engines armed with nuclear lasers and fuel. The black hole would add at least another million tons and all of its fuel, all the relevant supplies, and supporting spacecraft would bring the total mass of our interstellar craft to something in the neighborhood of 4 million tons. Depending on its configuration, it could be close to 1,000 or so meters long which is just about two thirds of a mile, and about a quarter of a mile across. Sounds huge and very, very expensive, doesn’t it? And this baby goes from zero to ~0.5c in just 6.3 months! How could alien astronomers not notice something like that screaming through the voids of space, warping the photons from the sunlight behind it and leaving a high speed smear in the spectrum of our sun on its way out? Well, for the size and speed of this thing, you have to remember that its traveling through space and as such is tiny if we’re going to compare it to the kind of objects telescopes can actually resolve. We have trouble imaging gas giants in other solar systems, gas giants which are 50,000 times bigger than our hypothetical ship. Sure, its wake is going to affect how the spectrum of a star looks but the warping would be so tiny that it may not even be visible as an artifact of the imaging process, the tiniest fraction of a pixel across, smaller than an exomoon.

And that’s the real gotcha in an otherwise interesting plan. Even if you’re lucky enough to catch an alien ship in the middle of crossing between two nearby solar systems and snap that one in a quadrillion shot, how exactly do you prove that this microscopic smudge in the spectrum is the trail of an extraterrestrial spacecraft? What says it wasn’t dust in the air or atmospheric fluctuations at the time of the shot? Even if you take a picture with an orbital telescope to avoid having a stray air particle from blotting out a snapshot of a relativistic craft, there’s still the potential of a microscopic speck of space debris or a wandering electron to mess with the shot. If the alien species in question build a ship the size of Mercury and flies past our solar system, we’d probably have some chance of catching their relativistic wake by happenstance. Otherwise, the ship will be just too small for a proper identification, if would even register in the image in the first place. Likewise, if we set our sights on a few dozen nearby stars floating close to each other, we wouldn’t necessarily boost our odds of seeing aliens traverse between them since we have no guarantee that they would evolve and thrive in those systems, just a vague estimate of probability that a planet supporting life in general may exist there. It seems that if we’ll ever catch ET mid-flight, it would’ve had to buzz our telescopes on its way to planets unknown…

Ever since Giovanni Schiaparelli saw what he termed canals on Mars, we’ve been expecting the red planet to be home to an advanced alien species, often presented as little green men and women encased in metallic, bulky suits in pop culture. Yes, the canal business may well have been a misunderstanding on the part of the translators since Schiaparelli may have meant completely natural gullies, but then again, he never corrected reports claiming evidence for life on Mars as evidenced by the blurry, waterway like features spanning across a good deal of the planet. Science fiction quickly seized on the news and many a novel about a dry and slowly dying world populated by a complex, intelligent civilization either waiting to be rescued, or decaying into chaos and war over dwindling resources were written, portraying the canals as either their last-ditch effort to save all that was still left, or the ruins of their heyday. You could say that we’re primed for the notion of life on Mars and every discovery of water in its past seems to hint at the chance of something living, even if it’s only microbes buried deep under the barren, inhospitably radioactive surface. But where are all these microbes hiding?

In the latest iteration of water without life cycle, the ESA reports that once upon a time, Mars had an enormous ocean if not two covering much of its northern hemisphere, one a billion years after the other. While Earth is still cooling down from its collision with Thea and giving birth to continents, Mars is developing vast oceans in which life can flourish. Unfortunately, in its smaller gravity and thin atmosphere, all that water would be frozen in just a million years if it hadn’t evaporated before that, too fast for life to form according to some. Just to add insult to injury, the oceans may have been extremely salty, so salty that some astrobiologists doubt that life could even survive in these conditions. And going by this train of thought, we have to conclude that life we can understand never even got a chance to take root on Mars, much less grow and diversify. Or do we? After all, a hypersalene lake is not exactly a dead zone for all living things and we find hearty bacteria living there almost all the time. Likewise, a million years in not exactly fast and for microbes with life spans of days if not hours, a few billion generations can come and go. Since evolution works by generation rather than by time, they would evolve at warp speed by comparison to macroscopic life and have a chance to adapt and survive.

Furthermore, since we’ve never seen an alien life form and don’t know how long it took for life to arise here on our own world, how can we be sure that for Martian microbes, a million years is too little time to develop? How do we know if they weren’t already there before the oceans formed, using another source of water? True, it’s a lot more likely than not that these mirobes would be restricted to water as a solvent in their chemical reactions in their bodies because Mars is just not cold enough to liquefy gases that could be a substitute, but any other assertion about them could still be questioned. And since we haven’t exactly explored all of the red planet with a very clear idea for what we’re looking, it’s hard to definitively rule out that it may still host life. Obviously, we’re going to need to temper out expectations but at the same time, it may be wise to hold off on pronouncements of how long was long enough for life to get started on Mars and which resources it will and will not have. We’re still finding life in amazing, seemingly utterly inhospitable and alien places on Earth, and our primeval world’s environment, which we know for a fact was crawling with life, would be so harsh and alien to us, we would die from exposure to toxic gases and unbearable heat if we ever went back there in a time machine. Why not give Mars the same benefit of the doubt that we give our caves, ocean depths, and subterranean lakes?

Quite a bit of scientific literature on astrobiology is filled with references to very exacting criteria for exoplanets capable of sustaining alien ecosystems. They have to be just the right distance from their suns, have the right kind of atmosphere, fall in the right temperature range, and hopefully, have a large stabilizing moon to counter their constant orbital wobbles from creating ice ages and migrating ice caps around the poles. But as we see more exoplanets out in the wild and do more accurate simulations, we’re finding that a lot of these constraints are starting to fall away. It seems that life could have a chemical basis in a liquid ethane lake, and might not even need a star to host a habitable ocean. And now, it looks like it might not even need a big moon to keep its axis more or less steady over the eons, allowing complex life to evolve without swift climate changes. It’s a nice to have for a flourishing ecosystem, certainly, kind of like having traction control in your car is a really nice and helpful feature, especially on ice and wet roads. But you can certainly get by without it if you had to, just as potential alien life on exoplanets without a big moon like ours could cope with an occasional climate shift.

It all started with a simulation in 1993 which showed that without the Moon, our planet could wobble as much as 85° on its axis which means that long term climate patterns humans enjoyed for many thousands of years just wouldn’t be possible. On geologic timescales, we’d be looking at mass extinctions on a far more frequent basis than we see in the fossil record as life would struggle to adapt. Planets are not exactly dainty things and all this would happen over tens of millions of years, but if we consider that Earth was home to living things for roughtly 3.5 billion years or so, these are fairly rapid and extreme changes which would test evolution’s ability to produce complex multicellular organisms when the selective pressure is to stay small and very efficient. So if an alien planet wants to be home to a massive, complex, and diverse ecosystem, it better be just as stable as we are, wobbling only by 2.6° at most thanks to our massive Moon, right? Turns out that that’s not the case at all because the range found in the original study is actually exaggerated by more than a factor of two. In fact, if the Moon was never formed, we would’ve wobbled between an axis of 10° and 50° over 4 billion years. Not a bad improvement on the originally predicted arc that could turn our planet sideways, then upright again.

And there’s another surprise. Within those 4 billion years without the Moon’s influence, there are stable cycles lasting for 500 million years. While the planet’s orbital wobble would be far more extreme than we have now, it wouldn’t be anywhere near 85° off axis. A more accurate figure seems to be 15° or so, which would entail the occasional massive ice age followed by rapid warming periods, but on timescales that would span almost all the evolutionary changes that lead from giant sea scorpions, to dinosaurs, to us. How can this kind of stability be possible if we didn’t have a lunar rudder? Well, generally a planet wobbles due to the very slight tugs from other objects in the solar system accumulating over millions and millions of years. But the same tugs that will send a planet wobbling could also be corrective and the occasional comet or asteroid impact could nudge the planet in another direction by countering a tug from a distant world or a passing comet. It all ads up to a slow, almost reluctant wobble rather than uncontrolled tumbling through space. And if the planet happens to be in a retrograde orbit (orbiting in the opposite direction of its siblings), their wobbles are in the same range as our current axial oscillations. That means we can bravely widen our search to include rocky worlds without large, stabilizing moons as a potential home for macroscopic aliens, if not other intelligent life.

A recently trumpeted paper on astrobiology did some very interesting modeling in a search for places on Mars where some very tough terrestrial microorganisms could survive and came to a very surprising conclusion. It appears that some 3.2% of the red planet could be habitable by volume, which would make it more friendly to life than our seemingly idyllic world, a world which has been populated with countless living things for billions of years. Now, considering that the Martian surface is as inhospitable to life as it gets because it’s constantly bathed in radiation potent enough to kill even the most radiation resistant creatures we know to exist, all of this habitable alien real estate is underground, where the deadly rays can’t reach and the temperature and pressure are just right for liquid water to flow through porous rock. Good news, right? If we just dig enough, a future robot, or better yet, a human astrobiologist, should be able to find honest to goodness little aliens.

Yes, little green germs aren’t exactly the little green men of classic science fiction, but hey, at least they’ll be a real extraterrestrial organism and we’ll know for a fact that we’re not alone in the universe. If life could arise on two planets in the same solar system and might be swimming under miles of ice on a moon that looks like a better and better candidate for alien habitation every day, certainly the entire universe is teeming with all sorts of living things, right? Hold that thought. One of the big caveats of using these models as a definitive guide for alien hunting is the lack of detail. In their zeal to report a sensational story, most pop sci outlets just repeated the great statistic and used it as a tie in to Curiosity’s upcoming mission to track down where exactly Martian microbes would settle into a nice colony to call home. But the simulations merely looked at how far down into the red planet’s caves and rocks we could go and still find possible traces of liquid water. The question of an active, frequently stirred and replenished nutrient base for life to function was briefly mentioned in the paper’s disclaimers for future research, despite being the second main prerequisite for habitability.

Of course it’s perfectly fine for a scientific paper to focus on just one narrow question and leave tangents for a team interested in building up on its work. It’s only frustrating when a premise is obviously flimsy or just out of left field and all the important details are waived off as something for others to refine. But in this case, the pop sci news circuit neglected to mention that the authors only set out to see how far Martian rovers could keep on following the water, as per NASA’s strategy for finding life on the red planet, and reported their results as one, big, definitive model showing that Mars is actually more habitable to life than Earth by volume while all it really says is that under the Martian surface, liquid water should be quite plentiful if we extrapolate some models of our own subterranean conditions and ecology to our diminutive, red, desert cousin in the inner solar system, and does a fairly thorough job of establishing the reasoning behind this conclusion. The leap from where we could find water on Mars to declaring that the typically monolithic block known as "scientists" estimate that the caverns of Mars hold three times the habitable territory by volume than Earth from that conclusion was simply a sensationalistic over-exaggeration. We don’t know how truly hospitable to life Mars really is.

But all that said, Mars is a very promising target for extraterrestrial microbes and the curtain of radiation which makes life nearly impossible on its surface will actually aid in our search for them. As noted in the reference, leaving our equipment to soak up the powerful UV rays for a few hours would sterilize it and any biota found in caverns or after digging several dozen feet into the red soil is then extremely likely to be native rather than the forward contamination from our own world. And yes, that means we absolutely should go there and devote as many resources as possible to make walking on Mars a reality. Of course the R&D involved won’t only benefit astrobiologists since the necessary reactors, self-sustaining habitats, and treatments to combat the damage caused by constant exposure to radiation could generate tens of billions in revenues and profits for all of the companies involved in putting together the mission’s toolkits if they channel them into mass market products ranging from medical devices to infrastructure. Actually, come to think of it, maybe one of the best things we’d be able to do for the world’s fragile economy is to go on a hunt for some little green germs and test all the pop sci news friendly astrobiology papers like this one on the actual surface of another planet. We tried just about everything else at this point and it doesn’t seem to be working, so why not think outside the box for a bit?

Whenever you tell someone that you have trouble believing in an omniscient, omnipresent, invisible deity who created the universe by its sheer will, but you’re certain that there is alien life elsewhere in the cosmos, oddly, you will get surprised stares. How can you believe that aliens are out there? No one has seen them so what evidence do you have that they might exist? Well, besides the fact that for an alien to exist would take far fewer leaps of logic and far fewer assumptions, it’s because we keep finding the chemistry of life floating in deep space in nebulae and asteroids, and the recent set of observations from our telescopes keep turning up the signals of potential places for alien life to exist. While the discovery of Gliese 581g might have turned out to be less than meets the eye at first, we now have a confirmed detection of a seemingly hospitable place for a biosphere, the terrestrial world of Kepler-22b. It orbits a Sun-like star every 290 days, placing it firmly into the habitable zone where temperatures should be ideal for liquid water given an atmosphere of the right density, and it’s only some 2.4 times bigger than Earth, firmly in the realm of the kind of planets we want to find.

Of course we still don’t know a lot of things about Kepler-22b. Without a good idea of its composition, we can’t say what its gravity is like or what gases float in its atmosphere. Plenty of oxygen would immediately signal an abundance of life there. but even if we don’t detect oxygen, it doesn’t mean that its lifeless. After all, oxygen is a toxic and corrosive gas which quickly breaks down without being steadily added into an atmosphere by biota, and we now know that life can thrive on other gases, including methane and carbon dioxide. Just as long as a liquid is present as a solvent, some form of self-perpetuating chemistry can arise and sustain itself. Because the planet is about 600 light years away, even if it has a glowing alien city covering half of its hemisphere, we wouldn’t be able to see it since all of Kepler-22b would be only a tiny smidgeon of a single pixel in our highest resolution images, and without an obvious flag like a significant amount of atmospheric oxygen or other hard to sustain gas, we’d never really know whether Kepler-22b hosts life or not without actually going there to find out firsthand. However, even knowing that such a planet actually exists and shows so much promise is quite thrilling in and of itself, especially knowing that it’s been detected directly three times, unlike Gliese 581g.

True, we shouldn’t imagine it as an alien Eden yet, but it’s hard not to get excited given what we know about it so far, especially given the fact that it’s not the only planet we know of close to or in its parent star’s habitable zone. In fact, SETI is now calibrating its telescopes to include Kepler data and trying to listen for any trace of artificial activity leaking into space from the most promising worlds in this growing planetary catalog. We have been dillgently trying to see if we’re not alone for the last century or so, and we’re now gaining the tools to take a much deeper and more thorough look at our stellar neighborhood to see if there’s anyone out there. It’s not an area of research we should take lightly and we should continue to look for alien life within our solar system as well, with Europa being one of the best candidates for an extraterrestrial biosphere. Knowing that we’re not a lonely spark of life in the cosmos for a fact may not change life as we know it nowadays, but maybe one day, it may help us to see ourselves not as citizens of countries competing for dominance, but as a single species living on a fragile little world, Sagan’s pale blue dot, a species which needs to look aim skyward and refuse to stay content with having a short lifespan and its feet planted firmly on the ground. Our distant ancestors were explorers and inventors, and we owe it to them to continue their legacy, not wallow in the mundane minutia of post-industrial life, trapped under the heel of bureaucrats bereft of any vision or sense of wonder.

At the rate we’re going, it seems that the first target for one of our future interstellar spacecraft will just have to be the Gliese 581 system. Beyond the initial hype generated by the announcement of planet 581g and a very deflating set of calculations showing that it may have just been a mirage, there were still planets with a little potential for life as we can understand it. This is why when discussing the practicality of colonizing the solar system in question, I brought up two worlds which seem to have faded from our collective memories. Now, it seems that one of these worlds, 581d, may actually be the terrestrial, habitable planet for which astronomers have been searching. Originally thought too cold for liquid water, the planet was put on the back shelf until an advanced climate model ran by French scientists showed that such a world could actually have oceans, rain, and stay warm enough to avoid having its night side frozen solid if it were tidally locked in its orbit. How? Well, as it turns out, it all comes down to sunlight, or rather to the right wavelength of sunlight. For a big planet with an atmosphere rich in carbon dioxide, a red star may actually be an enabler of a dynamic, warm climate…

When astronomers first considered Gliese 581d as a candidate for habitability, they thought that much of the light from its parent star would be reflected back into space as happens on our world. However, the light we get from the Sun has a shorter wavelength and gets scattered when it meets air molecules and other small, fine particles in our atmosphere. This phenomenon called Rayleigh scattering and it’s what gives our skies a bluish tint. When dealing with longer wavelengths, like you’d find coming from oh say a red dwarf star, the red light scatters less and more of it reaches deeper into the kind of thick carbon dioxide atmospheres that seem common for large, rocky planets. As a result, the skies of Gliese 581d would have a murky reddish glow and the conditions would support a water cycle, which we know to be a key for enabling life. If this model is right, it would not only mean that a planet just over 20 light years away is habitable, but that it’s probably inhabited by something since it’s difficult to imagine a watery world without life. After all, once upon a time Earth’s air had a lot of carbon dioxide and other gases we consider noxious and deadly today while its oceans were home to a countless variety of bacterial colonies thriving for billions of years, reproducing and growing away while much of the planet was erupting away with vast lava flows and toxic plumes that made the surface unlivable.

Whether 581d is tidally locked or not could determine what could live there and where we could find traces of those living things. Having a perpetual day side could allow for constant photosynthesis for organisms which would form the base of food chains in which the lit hemisphere is the central hub of all activity. Life could exist on the night side as well, but if photosynthesis didn’t evolve on 581d, the base of the food chains would be an assortment of bacteria feeding off thermal vents on ocean floors. Were the planet to rotate around its axis and have an actual night and day cycle, we could expect living things to be more widespread as more habitats will be available to them. Either way, the entire planet would be warmed thanks to wind circulation, but with direct sunlight across 581d a greater variety of organisms may have chances to establish new footholds to escape predation or to take full advantage of abundant resources. This is after all how we think all our forests started out, as primitive plants which grew with no competition, feeding on sunlight and carbon dioxide. If 581d were to repeat this evolutionary step, we could find traces of some sort of biological activity in its atmosphere. This is all conjecture, of course, and further observations will need to be made to figure out more about this world, but since we now know its potential, we should devote some time and resources to study it.

Again, it should be noted that as far as interstellar objects go, Gliese 581 is very close by, close enough to be of interest to some sort of mission at some point in the future. Should our hunches turn out to be right, there’s a very strong case to be made for at least trying to send a probe there. It may take a very long time to come up with the required technology to make the trip quickly enough, but with a very reasonable target in sight, it may just motivate enough space agencies, scientists, and engineers to rise to the challenge and create the brand new generations of computers, engines, reactors, and materials required for the journey. Maybe discovering and confirming that 581d can support life is exactly what we need to motivate future space explorers. Though we also need to be very cautious not to get too attached to the idea that 581d must be habitable because the models may be wrong and we don’t want to let confirmation bias take over the astronomers’ observations. It’s fun to speculate and the models seem very promising thus far, but at the end of the day, real data will need to have the last word on whether Gliese 581d is really habitable or not.